A variety of technologies for storing data are available today with varying scope of application depending upon their cost, memory capacity and method of data access. Examples of data storage techniques associated with computer industry are floppy diskette, compact disc and semiconductor based memories.
Handling of manufactured goods and materials also require some form of data carrier device for their identification or surveillance from a distance. Their demand in terms of storage capacity is considerably lower than that required for computer industry. Two widely used methods for article identification and surveillance are printed optical bar-codes and magnetic-strips. Bar-codes are commonly used for identifying objects in shops and supermarkets. An application of magnetic strips is the credit card. The main reason for the popularity of bar-codes and magnetic strips is that they are inexpensive. The drawback of bar-codes and magnetic strips is that the reader has to have a physical contact or has to be very close, say a few centimeters, from the bar-code or magnetic strip to read. If there is no physical contact, then the space between the code and the reader should not have any obstruction and properly aligned for correct readability. This requires concentration from the part of the human operator and therefore is inconvenient.
RFID (radio frequency identification) is another technology for article surveillance and identification. RFID enables larger readability distance compared to that of the magnetic strip technology or the bar-code technology. The data is stored in an RFID system called RFID tag which once interrogated by the remote reader, return an encoded radio signal that contains the data. Different embodiments of RFID tags are disclosed, for example, in the following publications: U.S. Pat. Nos. 5,574,470; 5,625,341; 5,682,143; 5,995,006; 6,100,804; 6,346,884; 6,424,263; and 6,441,740.
RFID-tag devices can be broadly divided based on the criterion whether they contain an integrated memory chip or not. Those that contain a memory chip, e.g. U.S. Pat. No. 5,874,902, in general have larger memory capacity than those of chip-less tags, e.g. U.S. Pat. No. 6,708,881. However, chip based tags have a significantly higher cost compared to that of the chip-less tags.
RFID-tags can also be divided based on the criterion whether they contain a battery or not, denoted active and passive tags in the art. In general active tags, which are the most commonly available tags in market today, have a larger operational distance range when compared to the passive tags, e.g. U.S. Pat. No. 6,621,417.
Passive chip-less data carrier devices used in RFID tags have significant advantages in that they are passive, of low cost and enable readability at large distances. Furthermore, battery-free tags do not have the problem of limited life time and the need for battery exchanges.
The international application WO 2006/043876 discloses a passive chip-less data carrier device that comprises a powder divider having multiple output terminals connected to different branches. Each branch comprises a unique set of a time delay, a phase shifter and an attenuator. The output terminals of the branches are then combined in a power combiner.